The present relates generally to fiber optics, and more specifically to a method for making an attenuator.
Although a primary virtue of optical fibers as a communication medium is the low loss of the fibers, there are instances where it is necessary to provide attenuation in the path. U.S. Pat. Nos. 4,557,556 and 4,557,557 disclose methods of fabricating attenuator for optical fibers by fusion splicing. In the '556 patent, a fiber is cleaved, and the axes of the cleaved ends are offset and butted one another. The abutted offset ends of the fibers are melted and the axes of the cores of the melted abutted fiber ends are aligned by way of surface tension. This realigns the cores, except that the cleaved ends of the cores bend off the axis in opposite directions. The technique is said to be applicable to single-mode optical fibers, which are characterized by a core diameter of 8-10 microns and a cladding diameter of 125 microns.
In the '557 patent, the cleaved fiber ends are aligned and melted, and while the ends are in a plastic state, they are moved towards each other to distort the fiber ends. The cores bend slightly near their abutted ends and are partially or wholly misaligned to provide the attenuation. During fabrication, light is injected into one of the fibers and a receiver is coupled to the other fiber. Initial axial alignment prior to fusing is performed by maximizing the transmission through the abutting fibers. When the fibers are fused, the power level is monitored and movement is stopped when a desired level of optical loss is observed.